An optical waveguide (1) having a detour is disposed at either or both of the light-receiving and light-emitting ends of a dispersion optical system in a spectroscope. Even though light being propagated through the optical waveguide has specified polarizing characteristics, the light is depolarized by passing through the optical waveguide and many times reflecting therein. Accordingly, unpolarized light not affected by the polarization selectivity of the dispersion optical system (5) or the like can be emitted from the spectroscope.